Highly luminescent platinum(II) complexes based on pyrazolo[1,5-f]phenanthridine-containing ligands

A series of highly luminescent [Pt(NˆCˆCˆN)] emitters (ZPt1, ZPt2 and ZPt3) based on pyrazolo[1,5-f]phenanthridine-containing ligands were designed and synthesized. These Pt(II) complexes demonstrated extremely high thermal stabilities with the 5% weight-reduction temperatures over 450 °C due to the incorporation of the rigid pyrazolo[1,5-f]phenanthridine motif and the robustness of the tetradentate coordination framework. These Pt(II) complexes have the same coordination set (pyridineˆbenzeneˆbenzeneˆpyrazole) but with slightly different linkage between coordination groups. Within ZPt1 and ZPt2, pyridine and the neighboring benzene groups are separated by oxygen and aniline, respectively. In ZPt3, pyridine group is rigidly grafted on the carbazole unit. The effect of the different linkages on the frontier orbital energies, the photophysical and electroluminescent properties of ZPt1-ZPt3 was investigated systematically. Organic light emitting diodes (OLEDs) based on these Pt(II) complexes were fabricated with typical device structure. The Pt(II) complexes displayed intense electroluminescence in the blue to yellowish green spectral region. Among the three Pt(II) complexes, the 3-(pyridin-2-yloxy)phenoxy-based ZPt1 compound showed the highest electroluminescence performance with the maximum CE, PE, and EQE of 58.0 cd A⁻¹, 51.6 lm W⁻¹, and 16.4%, respectively.     

Highly phosphorescent platinum(II) complexes based on rigid unsymmetric tetradentate ligands

A new class of highly phosphorescent Pt(II) complexes (Pt1–Pt3) based on rigid unsymmetric tetradentate ligands (L1-L3) were designed and synthesized. L1-L3 ligands are an analogue to N,N-di(2-phenylpyrid-6-yl)aniline (L) except that one coordination phenyl group in L is replaced by other motifs with different electron donating/accepting capabilities. The effect associated with the modulation of a single coordination group within each ligand on the photophysical and electroluminescent properties of Pt1–Pt3 was investigated systematically. Among Pt1–Pt3, Pt1 has the highest HOMO due to the presence of a strong electron-donating group (3-methylindole), and exhibits the narrowest bandgap; Pt2 has the lowest HOMO due to the lack of strong donor group within the structure, and shows the widest bandgap. Organic light-emitting diodes (OLEDs) based on these three complexes showed yellowish green to greenish yellow electroluminescence with high efficiency. Notably, the device based on Pt1 at the doping level of 10 wt% achieved a maximum efficiency of 53.0 cd A⁻¹, 35.9 lm W⁻¹ and 16.3% with CIE coordinates of (0.44, 0.53).     

Computational studies of electronic structures and photophysical properties of luminescent iridium(III) complexes based on amidinate/bis(pyridylphenyl) ligands

To provide a deeply understanding of the nature of the emissive origin as well as the radiative and nonradiative processes, theoretical studies have been performed on four amidinate/bis(pyridylphenyl) iridium(III) complexes. It has been testified that they have exhibited bright yellowishgreen phosphorescence emission with moderate photoluminescence quantum yields. Besides geometries, electronic structure, absorption and phosphorescence spectra, and the factors governing the radiative decay rate constants of the emissive state have been examined. Additionally, this work also explores the potential energy profiles of the deactivation pathway via the triplet mental-centered states. Among these complexes, complex 2, which contains the bulky t-butyl group on the amidinate nitrogen atoms, presents the highest internal quantum yield. To explore more efficient phosphors, three novel phosphors, 2a, 2b, and 2c have been designed on the basis of complex 2 by incorporation of substituents on the bis(pyridylphenyl) ligand with a slightly higher quantum yield.     

Theoretical studying of basic photophysical processes in a thermally activated delayed fluorescence copper(I) complex: Determination of reverse intersystem crossing and radiative rate constants

The photophysical properties of a mononuclear Cu(dppb)(pz₂Bph₂) complex have been investigated by employing the thermal vibration correlation function (TVCF) approach. The harmonic oscillator model with origin displacement, distortion, and Duschinsky rotation effects for the potential energy surfaces are considered. Absorption spectrum obtained by the scalar relativistic density functional theory combined with restricted open-shell configuration interaction including spin-orbit coupling effects is in excellent agreement with the experimental data. We found that the intersystem crossing (ISC) from the first excited singlet state (S₁) to the triplet state (T₁) is forbidden by direct spin-orbit coupling at the first-order perturbation, but becomes allowed through combined with vibronic coupling. The reverse intersystem crossing (RISC) proceeds at a rate of K_RISC = 3.98 × 10⁸ s⁻¹ at room temperature 300 K, which is about 6 order of magnitude larger than the mean phosphorescence rate, K_{P, av} = 7.3 × 10² s⁻¹. At the same time, the ISC rate K_ISC = 3.06 × 10⁹ s⁻¹ is again about 3 order of magnitude larger than the fluorescence rate K_F = 6.47 × 10⁶ s⁻¹. This implies that the S₁ state can be populated from the T₁ state, TADF should be observed and TADF decay time is τ(300 K) = 2.32 μs by fitting calculation. But at 30 K, the situation will change. The RISC rate becomes very small, about K_RISC = 1.19 × 10¹ s⁻¹, while the ISC rate only decreases slightly from K_ISC = 3.06 × 10⁹ s⁻¹ to K_ISC = 1.93 × 10⁹ s⁻¹. As a consequence, the Cu(dppb)(pz₂Bph₂) complex is highly attractive candidates for applications of TADF.     

Triphenylamine-based trinuclear Pt(II) complexes for solution-processed OLEDs displaying efficient pure yellow and red emissions

Highly efficient phosphors are critical in solution-processed organic light-emitting devices (OLEDs). Multinuclear Ir(III) complexes containing more than one metal center have showed great potential in fabricating high performance OLEDs, yet the electroluminescent (EL) properties of multinuclear Pt(II) complexes are rarely studied. In this work, two neutral trinuclear Pt(II) complexes are synthesized based on the triphenylamine core bearing three bidentate ligand arms. Both the yellow emitter (PyTPt) and deep-red emitter (IqTPt) exhibit improved photoluminescent quantum yields (PLQYs) compared with their corresponding mononuclear Pt(II) complexes. Furthermore, the PLQYs of PyTPt and IqTPt doped films are increased to 0.63 and 0.47, respectively. The solution-processed pure yellow-emitting device based on PyTPt achieves impressively high external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 16.92%, 56.74 cd/A and 29.09 lm W⁻¹, respectively, which are among the best performance reported for the OLEDs employing multinuclear Pt(II) complexes. The solution-processed device based on IqTPt shows pure red emission with the peak EQE approaching 9.0%. Both PyTPt and IqTPt display much higher EL efficiencies than their corresponding mononuclear Pt(II) complexes. This work demonstrates that it is an attritive strategy to develop multinuclear Pt(II) complexes for high-performance OLEDs.     

Different orientation of the transition dipole moments of two similar Pt(II) complexes and their potential for high efficiency organic light-emitting diodes

The efficiency of organic light-emitting diodes (OLEDs) is especially limited by their low light outcoupling efficiency. An approach for its enhancement is the use of horizontally oriented emitter molecules with respect to the substrate. In this study we quantitatively determine the orientation of the optical transition dipole moments in doped films of two similar phosphorescent Pt(II) complexes having a linear molecular structure. These emitters are employed in OLED devices and their efficiency is analyzed by optical simulations. For an OLED with slightly more horizontally oriented emitter molecules an external quantum efficiency (η_EQE) of 15.8% at low current-density is realized, indicating a relative improvement of outcoupling efficiency of 5.3% compared to the isotropic case. However, a very similar complex adopting isotropic molecular orientation yields η_EQE of only 11.5% implying an imperfect charge carrier balance in the OLED device and a shift of the recombination zone. Furthermore, we highlight the enormous potential of horizontal molecular orientation of emitting molecules in OLEDs.     

Sustainable phosphorescence based on solution-processable and vacuum-sublimable cationic ruthenium(II) complexes achieved by counter-ion control

We designed and synthesized a novel series of red-emitting cationic ruthenium(II) complexes 1–6 with the same coordinated ruthenium(II) cation tris(2,2′-bipyridine)ruthenium(II) while different-sized negative counter-ions, namely chloride (1), tetrafluoroborate (2), hexafluorophosphate (3), perchlorate (4), tetrakis(pentafluorophenyl)borate (5) and tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (6), respectively. Their physicochemical characteristics including solubility, photophysical properties and electrochemical behaviors were fully investigated. Experiments indicated that introduction of bulky anions could effectively lower the molecular polarity and lattice energy of these ionic materials, improve their solubility in organic solvents, thus enable constructing solution-processed organic light-emitting diodes (OLEDs) based on complexes 2–6. Furthermore, complex 6 was demonstrated evaporable, owing to the electrostatic interaction strongly reduced by its anion with the largest steric hindrance and well-dispersed charges. We succeeded in the preparation of orange-red-emitting OLEDs fabricated by vacuum evaporation deposition thereof, achieving a maximum brightness of 5345 cd m⁻² with color coordinates of (0.51, 0.44). To our knowledge, this is the first report on sublimable cationic ruthenium(II) complexes, suggesting their great potential as a new material system for sustainable phosphorescence.     

Dependence of Pt(II) based phosphorescent emitter orientation on host molecule orientation in doped organic thin films

We report that the molecular orientation of a disk-shaped Pt(II) complex dopant in organic thin films is linearly proportional to the orientation of the host molecules. We ascribe this relationship to the parallel alignment of the Pt complex with the host molecules induced by a π-π interaction. This would be caused by their planar and conjugated structure, indicating that the intermolecular interaction and steric effect play an important role. This finding can be applied to obtain a horizontal emitter orientation, resulting in highly efficient OLEDs based on Pt(II) complexes.     

Tetradentate Pt(II) 3,6-substitued salophen complexes: Synthesis and tuning emission from deep-red to near infrared by appending donor-acceptor framework

Two novel tetradentate platinum (II) 3,6-substituted salophen complexes of Pt-2 and Pt-3 were synthesized and characterized, in which the substituted group is a donor (D) unit of 4,4′-di(tert-butyl)triphenylamine (Bu^tTPA) for Pt-2 and a donor-acceptor (D-A) framework of Bu^tTPA and benzothiadiazole (BT) for Pt-3. Their thermal, optophysical, electrochemical and electroluminescent properties were primarily investigated. It is found that the emission for this type of tetradentate platinum (II) complexes is tuned from deep red to near infrared by appending D-A framework under photo-excitation. As a result, Pt-3 presented a significant near infrared electroluminescence peaked at 703 nm in its doped polymer light-emitting devices (PLEDs). The maximum external quantum efficiency of 0.88% is observed in the Pt-3 doped PLEDs using a blend of poly(vinylcarbazole) and 1,3-bis(5-(4-(tert-butyl)phenyl)-1,3,4-oxadiazol-2-yl) benzene as the host matrix. Our work indicates that appending D-A framework into tetradentate Pt(II) salophen complex is a useful strategy to get high-performance near infrared emission for this type of tetradentate Pt (II) complexes.     

Exciton and Polaron Quenching in Doping‐Free Phosphorescent Organic Light‐Emitting Diodes from a Pt(II)‐Based Fast Phosphor

By introducing a neat Pt(II)‐based phosphor with a remarkably short decay lifetime, a simplified doping‐free phosphorescent organic light‐emitting diode (OLED) with a forward viewing external quantum efficiency (EQE) and power efficiency of 20.3 ± 0.5% and 63.0 ± 0.4 lm W^?1, respectively, is demonstrated. A quantitative analysis of how triplet‐triplet annihilation (TTA) and triplet‐polaron annihilation (TPA) affect the device EQE roll‐off at high current densities is performed. The contributions from loss of charge balance associated with charge leakage and field‐induced exciton dissociation are found negligible. The rate constants k_TTA and k_TPA are determined by time‐resolved photoluminescence experiments of a thin film and an electrically‐driven unipolar device, respectively. Using the parameters extracted experimentally, the EQE is modeled versus electric current characteristics of the OLEDs by taking both TTA and TPA into account. Based on this model, the impacts of the emitter lifetime, quenching rate constants, and exciton formation zone upon device efficiency are analyzed. It is found that the short lifetime of the neat emitter is key for the reduction of triplet quenching.     

NaK(E)态的离解和Na(3PJ)精细结构分支比

研究了Na(3S) +K(4S) +nhν→Na(3PJ) +K(4S) +(n - 1 )hν过程 ,激光频率ν调到Na共振跃迁的两翼 ,分支比定义为I(D1 ) /I(D2 ) ,I(D1 ) ,I(D2 )分别是NaD1 ,D2 线的强度 ,在K密度 2～ 8× 1 0 2 0 m-3 范围内 ,测量了从Na共振跃迁的蓝翼 30 0cm-1 到红翼 1 0 0cm-1 的分支比 ,得到了离解率之比和精细结构转移截面 ,在近翼 ,分支比与ν有很大的关系。用对Na3PJ 态共振激发的方法 ,也得到了精细结构转移截面 ,对结果进行了讨论     

Modulation of Solid‐State Aggregation of Square‐Planar Pt(II) Based Emitters: Enabling Highly Efficient Deep‐Red/Near Infrared Electroluminescence

The design of square‐planar Pt(II) complexes with highly efficient solid‐state near infrared (NIR) luminescence for electroluminescence is attractive but challenging. This study presents the fine‐turning of excited‐state properties and application of a series of isoquinolinyl pyrazolate Pt(II) complexes that are modulated by steric demanding substituents. It reveals that the bulky substituents do not always disfavor metallophilic Pt···Pt interactions. Instead, π–π stacking among chelates, which are fine‐tuned by the associated substituents, also exerts strong influence to the metal‐metal‐to‐ligand charge transfer (MMLCT) transition character. Theoretical calculations indicate that Pt···Pt contacts become more relevant in the trimers rather than the dimers, especially in their T₁ states, associated with a change from mixed ³LC/³MLCT transition in the monomer/dimer to mixed ³LC/³MMLCT transition character in the trimer. Electroluminescence devices affording intense deep‐red/NIR emission (near 670 nm) with unprecedentedly high external quantum efficiency over 30% are demonstrated. This work provides deep insights into formation MMLCT transition of square‐planar Pt(II) complexes and efficient molecular design for deep‐red/NIR electroluminescence.     

Ni（pz）_4Cl_2型化合物的光磁性质理论研究

本文利用ｄ８（Ｄ＊４ｈ）全组态混合统一晶场理论对Ｎｉ（ｐｚ）４Ｃｌ２型化合物的吸收光谱、基态ＺＦＳ、ＥＰＲ参量及顺磁磁化率进行了统一的计算和理论分析．理论结果与实验观测值符合甚好，从而对Ｎｉ（ｐｚ）４Ｃｌ２的光、磁性质作出了完整的、合理的理论解释。     

掺Cr,Ni对S在Fe(100)面吸附的第一性原理研究

基于密度泛函理论(DFT)的第一性原理方法,在广义梯度近似下计算了Fe中掺Cr或Ni时S原子在Fe(100)面吸附的结构和电子性质,并计算了其分子轨道和吸附能。结果表明:S原子均是吸附在H位最稳定;纯铁时S在Fe(100)面H位的吸附能为-7.70 eV,掺Ni时S原子在H位的吸附能为-7.35 eV,吸附能的相对变化为4.5%;掺Cr时S原子在H位的吸附能为-5.79 eV,吸附能相对纯铁时变化为24.8%,表明掺Cr对S原子在Fe表面的吸附抑制作用更大。对比分析了每种吸附情况下的分波态密度,结果发现掺Cr时具有较高的局域电子云重叠,从而产生的排斥作用抑制了S原子的吸附。     

光折变晶体Bi12TiO20的折射率和光学均匀性的测量

本文报导光折变晶体Ｂｉ１２ＴｉＯ２０的折射率和光学均匀性的测量结果。     

Tuning the color and phosphorescent properties of iridium(III) complexes with phosphine-silanolate ancillary ligand: A theoretical investigation

A series of Ir(III) complexes [(CˆN)₂Ir(PˆSiO)], where (CˆN)H is 2-phenylisoquinoline (1), 2-phenylpyridine (2) or 2-(2,4-difluorophenyl)pyridine (3), and (PˆSiO)H is an organosilanolate ancillary chelate with either diphenylsilyl (a) or dimethylsilyl (b) substituent, are investigated by means of the density functional theory/time-dependent density functional theory (DFT/TD-DFT). Their relationship between structure and property is evaluated by the geometries, electronic structure, and absorption and phosphorescence spectra associated with the internal quantum yield. The effect of different substitutions on the ancillary ligand is explored by compare of the complexes 1a (2a/3a) and 1b (2b/3b). Furthermore, five complexes, 2b-1, 2b-2, 2b-3, 2b-4, and 2b-5, are newly designed by introduction of the substitution groups on the phenyl rings of the 2b (See Fig. 1). The theoretical result estimates that the complexes 2b-1, 2b-2, 2b-4, and 2b-5 would be the blue-emitting phosphors. Especially, the complex 2b-1 has a higher quantum yield relative to 2b by comparison of the factors governing the radiative decay rate constants of the emissive state and the feasibility of the deactivation process from the T₁ state via triplet metal-centered (³MC) state.     

Exploring the influence of different ancillary ligands of heteroleptic Ir(III) complexes on the phosphorescent properties: Emissive rule and photodeactivation dynamics

The complexity of emissive process for five heteroleptic Ir(III) complexes (dfpypy)₂Ir(LˆX), where dfpypy = 4-methyl-2',6'-difluoro-2,3'-bipyridine and LˆX = picolinate (1), dipivaloylmethanate (2), picolinic acid N-oxide (3), N,N'-di-tert-butylbenzamidinate (4), or 5-(4′-methylpyridine-2'-yl)-3-trifluoromethyl-1,2,4-triazole (5) (See Fig. 1), is unveiled by density functional theory (DFT) and quadratic response (QR) time-dependent (TD)DFT calculations including spin-orbit coupling (SOC). Besides the emission wavelength, we would like to pay intense attention on the emissive rule. It is found that the emission likely originates from different triplet states rather than only from the lowest Kasha state for complexes 1, 2, 3, and 5, which indicates they obey dual emission scenarios. In contrast, complex 4 follows the Kasha rule. Different from the total qualitative study, the quantum yield is semi-quantitatively determined in this work. The radiative decay rate constants (k_r) from possible emissive states are quantitatively determined by the quadratic response method. The triplet potential energy surfaces are constructed to elucidate the factors that affect the temperature-dependent nonradiative rate constants (k_nr). Complex 4 have the higher quantum yields in all the investigated complexes because of the larger k_r and smaller k_nr. The metal-centered (³MC) triplet state in the deactivation pathways is confirmed to play a vital role in determining the quantum yield.     

Pure and zirconium-doped manganese(II,III) oxide: Investigations on structural and conduction-related properties within the Lattice Compatibility Theory scope

Manganese(II,III) oxide Mn₃O₄ thin films have been deposited on glass substrates using a simple spray pyrolysis method. Zirconium doping protocol was applied in order to verify some recently claimed enhancements of hausmannite physical properties. Gradual doping was achieved with ratio [Zr]/[Mn]=1%, 2% and 3% in addition to pure Mn₃O₄. Beyond classical characterization techniques, effects of Zr-doping were studied in reference to the expected use in rechargeable batteries and sensing devices. Moreover, additional opto-thermal investigation and analyses of the Lattice Compatibility Theory led to a founded understanding to the dynamics of Zirconium ion incorporation inside Mn₃O₄ host matrices.     

Influence of high growth rates on evaporated Cu(In,Ga)Se2 layers and solar cells

Thin film solar cells based on polycrystalline Cu(In,Ga)Se₂ were prepared by elemental co‐evaporation using modified three‐stage processes on soda lime glass substrates at a low substrate temperature of 450°C intended for application on polyimide foils. The growth rates in the different stages of the growth process were varied, and it was observed that the final composition profile and structural quality of the film are mainly determined by the growth rate in the third stage. Application of high growth rates in the second stage was found to have no significant impact on layer morphology and gallium grading profile, which was confirmed by scanning electron microscopy, secondary ion mass spectroscopy, and x‐ray diffraction measurements. On the other hand, scanning electron microscopy cross sections revealed that high growth rates in the third stage lead to a fine‐grained structure toward the surface as well as smaller grains toward the back contact. Secondary ion mass spectroscopy and x‐ray diffraction measurements of such layers revealed a pronounced gallium grading profile, while Raman spectroscopy showed strong occurrence of group III‐rich phases in the near‐surface region. The final device performance was found to deteriorate by about 10% relative to the baseline process efficiency when growth rates of up to 500 nm min⁻¹ were applied in the second stage or 600 nm min⁻¹ in the third stage. Copyright © 2011 John Wiley & Sons, Ltd.     

In-situ spectroscopic study of the As and Te on the Si (112) surface for high-quality epitaxial layers

A detailed analysis of the As-exposed Si (112) and subsequent Te exposure was performed. X-ray photoelectron spectroscopy shows that the Te- and As-exposed Si (112) surface had 70% As and 27% Te coverage, respectively. Direct surface coverage measurement with ion scattering spectroscopy (ISS) shows that the Si (111) surface is completely covered by As, and that of the Si (112) had about 78% and 20% coverage of As and Te, respectively. Finally, using ISS shadowing effects, it was found that the Te atoms were positioned mainly on the step edges.